Tool tips

Considering that ASP/PHPR is great at displaying a lot of data, it would be very useful to be able to add -may be at field or row level- a tag for pre-defined values. Example: a table displaying a set of options and values. Say the table was already too large to display another column (description for each option), a dynamic tootip feature would come quite handy in here. Such features are mostly used for advertising purposes but can be very helpful additions to large tables to display additional information where needed.
Something like this java script: http://www.aspfree.com/c/a/ASP.NET/Programming-an-InText-Advertising-System-under-ASPNET-35/1/